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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,117 records · Page 62
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Frequency of fast, narrow gamma-ray bursts

A duration histogram for 24 gamma-ray burst events detected by an ISEE-3 experiment is presented which suggests the existence of two gamma-ray burst populations. A distribution is also shown of 123 Venera 13 and 14 events which suggests two such populations in each experimental sample, the domains separated with a minimum near 1 or 2 sec. It is pointed out that the results of the Goddard ISEE-3 gamma-ray burst spectrometer actually enhance the appearance of two burst populations suggested in the Venera data.

Norris, J. P.↗
NASA NTRS1984

The IRAS fast-moving object search

The IR Astronomy Satellite (IRAS) mission has yielded an all-sky IR survey with a detailed pointing history. An analysis is being conducted which will allow an estimate to be made of the detectable population of comets and Apollo asteroids. On the basis of results obtained to date, it is expected that IRAS will detect comets having visual magnitudes lower than 17 if their motions are greater than about 1 arcmin/hour. The positional accuracy of such detections depends on the number of bands in which an object was observed, although the accuracy has so far proved unsuitable for orbit determination. There is no evidence of an undiscovered main belt asteroid population at high ecliptic latitudes.

Davies, J. K.↗
NASA NTRS1984

Abundances and spectra of superathermal H(+), He(++) and heavy ions in a fast moving plasma structure (plasmoid) in the distant geotail

An ISEE-3 Geotail Mission sensor has furnished data on a 16-min particle intensity increase in the distant magnetotail from which rest frame distribution functions have been deduced for 3-150 keV/amu H(+), He(++), and ions with a charge state greater than 3. The event was characterized by isotropic electron distributions and is identified as a tailward-moving plasmoid. These suprathermal ions are convected nearly tailward at an average speed of 1000 + or - 50 km/sec and have an energy density of 150 eV/cu cm. A crosstail expansion speed of about 80 km/sec is indicated.

Gloeckler, G.↗
NASA NTRS1984

How fast do Galilean satellites spin?

Each of the Galilean satellites, as well as most other satellites whose initial rotations have been substantialy altered by tidal dissipation, has been widely assumed to rotate synchronously with its orbital mean motion. Such rotation would require a small permanent asymmetry in the mass distribution in order to overcome the small mean tidal torque. Since Io and Europa may be substantially fluid, they may not have the strength to support the required permanent asymmetry. Thus, each may rotate at the unknown but slightly nonsynchronous rate that corresponds to zero mean tidal torque. This behavior may be observable by Galileo spacecraft imaging. It may help explain the longitudinal variation of volcanism on Io and the cracking of Europa's crust.

Greenberg, R.↗
NASA NTRS1984

A fast viscous correction method for full-potential transonic wing analysis

An analysis of the transonic flowfield around a three-dimensional wing is carried out using a strip method. Attention is given to the boundary layer growth in the streamwise direction. A viscous correction technique is defined for the TWING code for solving the full potential equations. A viscous ramp at the base of a shock is superimposed on the boundary layer displacement thickness generated by an integral boundary layer method. A relationship is then obtained between the effective displacement thickness and a vertical component of the surface velocity, a transpirational boundary condition. The viscous correction is found to be unnecessary in weak shock conditions but gives a better shock position and pressure distribution in a strong shock condition when compared with data from an ONERA M6 airfoil and the Hinson and Burdges (1980) Wing A.

Lee, S. C.↗
NASA NTRS1985

Fast Clock Recovery for Digital Communications

Circuit extracts clock signal from random non-return-to-zero data stream, locking onto clock within one bit period at 1-gigabitper-second data rate. Circuit used for synchronization in opticalfiber communications. Derives speed from very short response time of gallium arsenide metal/semiconductor field-effect transistors (MESFET's).

Tell, R. G.↗
NASA NTRS1986

Fast Reed-Solomon Decoder

High-speed decoder intended for use with Reed-Solomon (RS) codes of long code length and high error-correcting capability. Design based on algorithm that includes high-radix Fermat transform procedure, which is most efficient for high speeds. RS code in question has code-word length of 256 symbols, of which 224 are information symbols and 32 are redundant.

Liu, K. Y.↗
NASA NTRS1986

Modular, Fast, Two-Dimensional Cyclic Convolver

Proposed high-throughput, real-time synthetic-aperture-radar (SAR) processor built using new, modular, two-dimensional cyclic convolver architecture based on polynomial factorization and designed for very-large-scale integrated (VLSI) circuitry. New architecture reduces cost, size, and power dissipation of SAR processor in comparison to high-speed array-processor approach. Processor also used for other image-and data-processing applications involving two-dimensional Fourier transforms.

Liu, K. Y.↗
NASA NTRS1986

Fast-Response Oxygen-Monitoring and Control System

Oxygen sensor is Y2O3-stabilized ZrO2 ceramic disk maintained at 843 degrees C. Overall system response time reduced to about 0.2 second, equal to or less than 1 percent of tunnel run time. When test gas oxygen concentration differs from normal air concentration by 25 percent or more, alarm sounds, and emergency tunnel shutdown signal operates. New ZrO2 sensors intended for hypersonic-vehicle testing.

Singh, J. J.↗
NASA NTRS1984

A fast hidden line algorithm with contour option

The JonesD algorithm was modified to allow the processing of N-sided elements and implemented in conjunction with a 3-D contour generation algorithm. The total hidden line and contour subsystem is implemented in the MOVIE.BYU Display package, and is compared to the subsystems already existing in the MOVIE.BYU package. The comparison reveals that the modified JonesD hidden line and contour subsystem yields substantial processing time savings, when processing moderate sized models comprised of 1000 elements or less. There are, however, some limitations to the modified JonesD subsystem.

Thue, R. E.↗
NASA NTRS1985

Fast approach for calculating film thicknesses and pressures in elastohydrodynamically lubricated contacts at high loads

The film thicknesses and pressures in elastohydrodynamically lubricated contacts have been calculated for a line contact by using an improved version of Okamura's approach. The new approach allows for lubricant compressibility, the use of Roelands' viscosity, a general mesh (nonconstant step), and accurate calculations of the elastic deformation. The new approach is described, and the effects on film thickness, pressure, and pressure spike of each of the improvements are discussed. Successful runs have been obtained at high pressure (to 4.8 GPa) with low CPU times.

Houpert, L. G.↗
NASA NTRS1984

A fast, programmable hardware architecture for the processing of spaceborne SAR data

The development of high-throughput SAR processors (HTSPs) for the spaceborne SARs being planned by NASA, ESA, DFVLR, NASDA, and the Canadian Radarsat Project is discussed. The basic parameters and data-processing requirements of the SARs are listed in tables, and the principal problems are identified as real-operations rates in excess of 2 x 10 to the 9th/sec, I/O rates in excess of 8 x 10 to the 6th samples/sec, and control computation loads (as for range cell migration correction) as high as 1.4 x 10 to the 6th instructions/sec. A number of possible HTSP architectures are reviewed; host/array-processor (H/AP) and distributed-control/data-path (DCDP) architectures are examined in detail and illustrated with block diagrams; and a cost/speed comparison of these two architectures is presented. The H/AP approach is found to be adequate and economical for speeds below 1/200 of real time, while DCDP is more cost-effective above 1/50 of real time.

Bennett, J. R.↗
NASA NTRS1984

Discrete orthogonal function expansions for non-uniform grids using the fast Fourier transform

A technique for applying discrete Fourier series to infinite domains is presented. The technique uses mappings designed to minimize truncation error and can be applied to solve mixed initial boundary value problems among others. The method is alias-free and yields consistent differentiation and integration operators. The mapping-induced truncation error is explicitly expressible and small in nearly all cases of interest. The method is illustrated for three problems involving convection, diffusion, and vortex interaction.

Cain, A. B.↗
NASA NTRS1985

A fast efficient implicit scheme for the gasdynamic equations using a matrix reduction technique

An efficient implicit finite-difference algorithm for the gasdynamic equations utilizing matrix reduction techniques is presented. A significant reduction in arithmetic operations is achieved without loss of the stability characteristics generality found in the Beam and Warming approximate factorization algorithm. Steady-state solutions to the conservative Euler equations in generalized coordinates are obtained for transonic flows and used to show that the method offers computational advantages over the conventional Beam and Warming scheme. Existing Beam and Warming codes can be retrofit with minimal effort. The theoretical extension of the matrix reduction technique to the full Navier-Stokes equations in Cartesian coordinates is presented in detail. Linear stability, using a Fourier stability analysis, is demonstrated and discussed for the one-dimensional Euler equations.

Barth, T. J.↗
NASA NTRS1984

A fast time domain digital simulation technique for power converters - Application to a buck converter with feedforward compensation

Small signal analysis was performed earlier to demonstrate the marked improvement of dynamic properties and stability margins of a switching regulator employing a novel feedforward input filter compensation scheme. A large signal nonlinear recurrent time domain model is presented for the converter to analyse the transient response due to a step input change with and without the presence of the proposed feedforward loop. The results are verified with experimental data.

Kelkar, S. S.↗
NASA NTRS1984

Fast numerical calculations of EHD sliding traction forces Application to rolling bearings

Based on analytical calculations assuming isothermal elastohydrodynamic (EHD) lubrication conditions, and on curve-fitting of a thermal correction factor, a new formula is proposed to calculate the sliding traction force developed in a concentrated contact, assuming a nonlinear, viscoelastic lubricant and undirectional sliding. When sliding occurs in the rolling and transverse directions (bidimensional sliding), a simplified numerical method is outlined by which the components of the local shear stress are quickly calculated. The latter method is applied to the calculation of the shear stress and temperature distribution in the ball-raceway contacts of an angular-contact ball bearing. Because of the viscoelastic behavior of the lubricant, a nonzero lateral traction force is obtained.

Houpert, L.↗
NASA NTRS1985

Fast laser-induced aerosol formation for visualization of gas flows

A technique for aerosol seeding of gas flows by laser-induced particle formation is demonstrated using a pulsed Nd:YAG laser (1.06 microns) for optical breakdown of a mixture of SF6 and H2 in an inert carrier gas. It is noted that, contrary to the smoke-wire approach, the laser-induced particles form first in zones of high turbulence, since mixing enhances coagulation. The method also allows seeding to be performed in locations hardly accessible otherwise and is mechanically nonintrusive. Finally, a study of the mixture and the breakdown effects indicates that for H2:SF6 ratios between 3:1 and 15:1 the particle formation is only limited by the physics of the gas/particle conversion.

Hassa, C.↗
NASA NTRS1984

Steps towards 8m honeycomb mirrors. V - A method for polishing aspheres as fast as f/1

The present method for the polishing of near-f/1 aspherics employs a lap whose shape is continuously changed under computer control as it moves over the rigid mirror blank. Required changes of radius, astigmatism, and coma in a circular lap are accomplished by means of edge-bending levers and tensioning members that use screw actuators. Attention is given to the case of an f/1, 8-m diameter paraboloid whose mirror blank has been cast in a centrifugally stressed, rotating furnace to within 1 mm of the desired optical figure. Attention is also given to the mechanical design of the active lap.

Angel, J. R. P.↗